An example of a device for providing a compensated measurement of the level of a liquid in a tank is disclosed in the international patent application publication no. WO2005038415. The device in WO2005038415 comprises a transducer for transmitting and receiving acoustic signals, and a waveguide connected to the transducer and extending into the liquid. The liquid level is basically determined based on the speed of sound and the transit time of the acoustic signal from the transducer to a surface of the liquid (where it is reflected) and back to the transducer again. Since the speed of sound depends on gas composition and temperature which may vary from time to time, the current speed of sound is used in determining the liquid level, which current speed of sound in turn is determined by means of a reference system in the waveguide. Further, since the gas composition and temperature in the reference system may differ from the gas composition and temperature in the rest of the waveguide above the liquid, for instance if the liquid level is low, a fuel pump associated with the tank is used to feed a flow of fluid (namely fuel) originating from the tank into a portion of the waveguide which in use is located above the liquid. The flow of fuel levels the temperature and gas composition, and consequently the speed of sound, throughout the waveguide above the liquid, which in turn allows for a more accurate measurement of the liquid level.
However, the device in WO2005038415 relies on the fuel pump to provide the flow of fluid, which may require extensive and costly modifications of the fuel pump and the associated tank when installing the measurement device.